May08-22 Senior Design Presentation

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May08-22 Senior Design Presentation

• Electronic Automobile Fluid Level Sensor

2
Team Members

• Team
• Nick Johnston, Team Leader
• Alex Garr, Communications Coordinator
• Drew Combs
• Dan Dillon
• Client
• Chris Justice
• Faculty Advisor
• Dr. Jiming Song

3
Planning

• Problem Statement
• The current method for measuring engine oil level
  is messy, time consuming, and inconvenient.
• Market survey
• No simple replacement for the conventional
  dipstick exists.
• Several measurement methods were considered.
• Capacitive sensor is small, cheap.

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System

• System description
• Sensor sends reading to measurement circuit
• Measurement circuit sends signal to
  microcontroller
• Microprocessor determines oil level, displays
  reading
• User interface tells microcontroller when to read
  data
• Calibration gets input from user, reads data from
  sensor, and stores settings in microcontroller

Block Diagram
Concept Drawing
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Functional Requirements

• Pressing the measure button shall return a
  reading within 3 seconds
• The device shall correctly measure whether the
  oil is below, within, or above acceptable limits
• The proper LED shall remain lit for 15 seconds
• The devices shall provide over 300 oil checks on
  one battery.

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Non-Functional Requirements

• Sensor components immersed in oil shall withstand
  220 F
• Device shall not require any external power
  source
• Device shall work regardless of orientation
• Sensor shall not degrade or introduce harmful
  substances into the engine
• User shall be able to drop in the device in place
  of current dipstick with no modification to
  vehicle
• All currents within the device shall not exceed
  50 mA
• All voltages within the device shall not exceed 3
  V

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Project Plan

• Microsoft Project used to generate work breakdown

• Deliverables
• Proof-of-concept prototypes
• Sensor schematics, PCB layouts
• Software design documents
• Risks involved

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Block Diagram
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Design Method

• Capacitive Sensor
• A sensor which is placed on the end of a dip
  stick to measure the level of oil through by
  seeing how much capacitance the sensor outputs.
• Capacitance Measuring Circuit
• This circuit uses a 555 timer which is dependent
  on a sole capacitive value to create a square
  wave output. The square waves frequency is
  dependent on the capacitive value and preset
  resistor values.
• Microcontroller
• The microcontroller then is able to count the
  pulses in the square wave to determine its
  frequency and the level of oil. The
  microcontroller will then output the
  corresponding value to the user interface.

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Software Specification
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UI Specifications

• 3 LEDs Red, Yellow, Green
• 2 Button Measurment, Hard Reset
• red need gt 1 quart
• yellow need ½ quart
• green good
• red flash too much oil
• green/yellow flash measuring
• All LEDs flashing calibrating
• measurement button press to take a measurement,
  hold to calibrate
• hard reset button press to reset entire system,
  possible transient hardware/software faults

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Testing Specification

• Software
• white box
• black box
• code analysis
• Hardware
• component
• system
• Integration
• black box
• microwave
• heat

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Circuit Diagram
This is the overall circuit which can be
separated and examined in 3 different blocks The
microcontroller, the capacitance measuring
circuit, and the capacitive sensor
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Capacitance Measuring Circuit
The circuit diagram to the left is the
capacitance measuring circuit. This circuit uses
a 555 timer to create a square wave which is
dependent on the capacitance of C4. C4 will be
the capacitance gathered from the capacitance
sensor. In this way we are able to tell the
change in capacitance by relating it to the
change in frequency of the output.
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Sensor Layout

• Cadence Layout Plus used for design drafting.
• Narrowest possible traces (6 mil) to maximize
  capacitance surface area and resolution.
• Use of both sides of the board so traces can be
  as wide as possible.
• Differential design so that outside influences
  will have minimal effects on reading.

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Sensor Principles

• Measures Capacitance of the area surrounding the
  sensor.
• Fringe effect capacitance is the primary amount
  of capacitance measured.
• As an object with a higher dielectric constant
  approaches the sensor, the total capacitance of
  the circuit increases.
• Minimal distances between traces lead to greater
  effects on capacitance due to the oil surrounding
  the sensor.

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Sensor Application

• The sensor is attached the end of an OEM
  equivalent dipstick and is submersed in the oil
  of the automobile engine.
• There are five capacitive circuits on the board.
• Each circuit will be polled numerous times by the
  microcontroller to gain an average capacitance
  per circuit.
• Finding the greatest difference in capacitance
  between two adjacent circuits determines where
  the oil level is.
• The differential design allows for repeatable and
  accurate results despite changes in oil
  temperature, oil quality, and the external
  environment.

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Software Design (1/2)

• Powerupvoid Init()Sets the power mode to the
  higher power, operational state.
• Powerdownvoid Shutdown()Sets the power mode
  to the lowest power state.
• Calibrationvoid mainCal() Main calibration
  routinevoid setCalData(char data, char stage)
  Saves the calibration data into nonvolatile
  memoryvoid blockInterrupt() Wait until the
  pushbutton interrupt arrives

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Software Design (2/2)

• Measurementvoid mainMeasure() Main measurement
  routinechar interpolate( char data ) The
  returned value is the relative oil level based
  off interpolated calculationsUIControlchar
  buttonPressed() Determines whether or not the
  button is pressed.void LEDController( char
  active, char blink) Two LED mapped characters
  are set to either activate or blink
  LEDs.SensorInterfacechar pollSensor() Sets
  the lines to poll the sensor and return the raw
  data

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Microcontroller

• TI-MSP 430 chipset
• Suggested by customer
• Chosen Model MSP430FF1101A
• Needed small amount of flash memory
• 1KB program memory
• 128B flash memory
• 128B ram
• Two I/O, 8-bit and 6-bit buses

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The CR2032 Battery

• One 3 Volt battery gives significant voltage and
  power for use in our embedded system.
• A Lithium battery
• Chosen for its small and slim like size

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Summary Of Work

• Nick Johnston 76.5
• Dan Dillon 76
• Drew Combs 63
• Alex Garr 68
• Created engineering project plan and design
• Started implementation of hardware and software
  designs

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Questions?